Enabling communication between a mobile communication device and one or more base stations is largely dependent on the ability to coordinate the timing of the mobile device with the timing of the base station(s). Toward this end, base stations are conventionally configured to communicate at a standard frequency or set of frequencies that may be defined for example, in an industry standard such as the TIA-EIA-136 standard or the standard that governs communication within a GSM communication system. In addition, base stations are configured to communicate using signals that are formatted according to a communication protocol that is also defined via the communication standard in use. For example, communication is typically defined to be cyclical in that each communication signal comprises a series of data frames having a defined format. Specifically, each frame is typically defined to include a fixed number of data symbols and a fixed number of time slots during which predefined forms of communication may occur. The time slots may comprise one or more receive slots during which the mobile communication device may be designated to receive information transmitted by the base station and one or more transmit slots during which the mobile communication device may be designated to transmit information to the base station. Thus, after a first frame comprising, for example, a receive slot and a transmit slot, the cycle repeats, i.e., another frame having a receive slot and a transmit slot follow.
As a result, the duration of each frame is equal to the smallest amount of time before the communication cycle repeats. Due to the cyclical nature of the communication signal and because the positions within a frame at which the receive and transmit slots are located may be fixed relative to the start of the frame, once the mobile device determines where the start of a frame occurs within a communication signal, the mobile device may synchronize to the frame start time so that subsequently transmitted frames are properly received. More particularly, once the start of a frame is identified, a system timer disposed in the mobile device synchronizes to the frame start and then generates control signals to control the timing at which various components disposed within the mobile device operate. For example, the system timer may generate control signals that enable a transmitter during the transmit slot and that enable a receiver during the receive slot.
Conventionally, system timers are configured to perform timing control by executing a set of software instructions that have been preprogrammed into the timer during manufacture. Thus, the conventional system timer may be programmed to operate according to a single predefined communication protocol. However, communication protocols are becoming more robust and are able to support a greater number and increasingly diverse set of signal formats. For example, mobile communication protocols that were once formatted exclusively to support the transmission of voice data are now being adapted to support the transmission of digital data. Unfortunately, the programming associated with conventional system timers is fixed such that the mobile communication device is limited to communicating in the protocol or format for which the system timer was originally programmed. In addition, system timers are currently used in a variety of different wireless communication devices that may each be adapted to operate according to different communication protocols. However, due to the preprogrammed, inflexible configuration of conventional system timers, a different system timer must be manufactured for each specific application.
Moreover, due to the mobility of a mobile communication device a system timer that has successfully synchronized to the base station may become unsynchronized due to movement of the mobile communication device relative to the base station. Specifically, the distance between a mobile communication device and a base station may vary when, for example, the mobile communication device is disposed in an automobile that is traveling either nearer or farther away from the base station and may adversely affect the timing between the mobile communication device and the base station and may cause interference between the signals being transmitted by the mobile communication device and signals being transmitted by one or more other mobile communication devices. More particularly, the base station assigns each mobile communication device disposed in a service area, referred to as a cell, associated with the base station a slot of time occurring at a specific location in a frame during which the mobile communication device may transmit signals for reception at the base station. However, a mobile telephone disposed in an automobile traveling toward the base station may generate signals that arrive at the base station earlier than the time slot assigned to that mobile communication device. Specifically, because the distance between the mobile station and the base station is decreasing as the automobile moves toward the base station the signal arrives earlier because the signal travels a shorter distance to reach the base station. Unfortunately, a signal arriving too early will interfere with a communication signal transmitted by a mobile communication device that has been assigned the earlier time slot. In contrast, a mobile communication device disposed in an automobile traveling away from the base station may generate signals that arrive at the base station later than anticipated because the distance between the mobile station and the base station is increasing as the automobile moves away from the base station so that the signal must travel a longer distance before reaching the base station. Thus, the signals that arrive at the base station late will interfere with communication signals transmitted by a mobile communication device that has been assigned to the later time slot. To combat this phenomenon, the base station is adapted to measure a timing delay associated with each mobile communication device communicating with the base station that represents the amount of time that a signal emanating from each mobile station is arriving either early or late. The base station then requests that each mobile telephone adjust the times at which information is transmitted to the base station by an amount of time equal to the time delay. When received at the mobile telephone, a microprocessor disposed in the mobile communication device may cause the system timer to use the timing delay to adjust the timing of the mobile communication device.
Conventional system timers are typically configured to use the timing delay information transmitted by the base station as it is received from the base station. Thus, timing delay information transmitted to the mobile communication device is supplied to the system timer at any time during the frame and often at multiple times during the frame. As a result, the system timer may interrupt the operation of the microprocessor or the digital signal processor several times during each frame to receive the delay data required for the timer to remain synchronous with the base station. Unfortunately, repeated interruptions unnecessarily burden the microprocessor/digital signal processor and unnecessarily limit the ability of the mobile device to perform at higher data rates.
Thus, there is a need in the art for a method and apparatus for controlling the timing at which a mobile communication device communicates that is adapted to execute instructions in a non-fixed order so that the mobile communication device may communicate different amounts of data using differently formatted signals. In addition, there is a further need in the art for a method and apparatus for controlling the timing at which a mobile communication device communicates that is able to compensate for movement of the mobile communication device relative to the base station in an efficient manner.